1. Field of the Invention
The subject matter of this invention relates generally to ground fault detecting systems and more particular to pulsating ground fault detection systems for polyphase electrical power distribution and transmission systems.
2. Description of the Prior Art
It is known to detect an electrical fault through the utilization of a transformer relay and an associated alarm in a ground line. Furthermore, the concept of utilizing a high resistance return line for ground fault current limiting purposes is known. Also, the broad concept of seeking the location of a ground fault is known. The broad concept of pulsing to detect faults is known as is shown in U.S. Pat. No. 2,721,307 issued to Bowels. Furthermore, U.S. Pat. No. 3,031,613, issued to Hojding shows a pulsing arrangement for a ground line in which a switch in the ground line is cyclically opened and closed to completely interrupt the ground fault current so that an operator can detect a ground fault in the system. In the Hojding case, however, a complete interruption of the ground fault current is necessary. In U.S. Pat. No. 3,343,080, issued to Fox, a ground fault system utilizing a broken delta in conjunction with pulsed serially connected resistors is taught for sensing ground fault current. The latter system teaches the use of an opened delta sensing transformer secondary winding. Other United States patents which teach concepts directly or indirectly related to ground fault detection, limitation and/or pulsing are as follows: U.S. Pat. Nos. 2,641,633 to Hosford, 3,287,636 to Gagniere, 3,230,424 to Gagniere, 3,176,219 to Behr, 2,403,414 to Traver, 2,400,749 to Foster. In addition, the following foreign patents disclose concepts of interest: British Patent Specification No. 923,292, German Pat. No. 1,144,839, and Norwegian Pat. No. 114,006. It would be advantageous if a current limiting pulsing-detector system could be provided which is basically the same for both delta and wye connected systems at both high and low voltages. Furthermore, it would be advantageous if the system were to utilize a pair of resistors, one of which would be permanently in place to limit current, and the other of which would be capable of being introduced in parallel with the first in an oscillatory or periodic manner so as to modulate or pulse the fault current. This would create detectable electromagnetic radiation in the line of the power system in which the ground fault current flows so that an indirectly connected detector could be utilized to determine the location of the fault current. This would be especially advantageous in high voltage situations where the system voltage may equal or exceed 2,400 volts.